For ruby Ports, I serve old to young. Younger ruby Ports - Vintage in particular - tend to be more powerful and more tannic which can overwhelm the older Ports if served later.
I don't think it matters all that much for tawny Ports, but I tend to serve the older ones first. Older tawnies tend to be more intense and concentrated which could theoretically overwhelm the younger ones that follow, but we're not talking the same degree of difference as you see in Vintage Ports. A young Colheita can still be intense, it just tends to be more on the vibrant end of the spectrum than those dark and brooding old timers.
I tend to separate TWAIOA and Colheita into groups, but more so that they can be compared to each other than any real need. I find that Colheitas need about 50% more age (maybe a little less) to reach the complexity of a blended TWAIOA, so these days an early '80s Colheita and a 20-year old Tawny would be roughly equal to me. Similarly, I find that a 40-yr old compares well with a Colheita from the '50s. TWAIOA tend to be rounder and richer, while Colheitas tend to be more focused and display more clarity. But they stand up to each other very well so I don't see any real need to separate them. It's just habit.
One good reason to serve the old stuff first - you're not drunk yet!
![Spent [kez_11.gif]](./images/smilies/kez_11.gif)
Serve the good stuff while you can really enjoy it.
